Leases (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 24, 2020 USD ($) lease restaurant	Jun. 26, 2019 USD ($) restaurant	Jun. 24, 2020 USD ($) restaurant lease	Jun. 26, 2019 USD ($) restaurant	Dec. 25, 2019 USD ($)	Dec. 27, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Operating Lease, Payments			$ 9,888	$ 13,015
Property held under operating leases, net ("ROU asset")	$ 184,308		184,308		$ 192,395	$ 205,200
Finance Lease, Right-of-Use Asset, Amortization		$ 3		9
Finance Lease, Interest Expense	5	7	11	15
Operating Lease, Cost	6,852	6,912	13,689	13,841
Short-term Lease, Cost	5	9	12	17
Variable Lease, Cost	150	154	279	322
Sublease Income	(763)	(511)	(1,541)	(901)
Total lease cost	6,249	$ 6,574	12,450	13,303
Operating Lease, Liability	$ 207,039		207,039		$ 213,898	$ 222,300
Finance Lease, Principal Payments			16	53
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			1,662	$ 4,995
Derecognition of ROU assets due to terminations, impairment or modifications			$ (558)
Number Of Finance Leases | lease	1		1
Number of Restaurants with lease modification | restaurant	4	3	7	3
Operating Lease, Lease Income	$ 100	$ 200	$ 300	$ 300
Impairment of Right-of-Use Assets			$ 543
Initial lease term	20 years		20 years
Operating Lease, Impairment Loss	$ 500	0	$ 500	0
Depreciation and amortization [Member]
Lessee, Lease, Description [Line Items]
Total lease cost	6	3	11	9
Operating Expense [Member]
Lessee, Lease, Description [Line Items]
Total lease cost	5,917	6,256	11,796	12,659
General and Administrative Expense
Lessee, Lease, Description [Line Items]
Total lease cost	119	114	230	233
Interest Expense
Lessee, Lease, Description [Line Items]
Total lease cost		7		15
Restructuring Charges [Member]
Lessee, Lease, Description [Line Items]
Total lease cost	$ 207	$ 194	$ 413	$ 387
Minimum
Lessee, Lease, Description [Line Items]
Lessor, Operating Lease, Term of Contract	3 years		3 years
Renewal term	4 years		4 years
Maximum
Lessee, Lease, Description [Line Items]
Lessor, Operating Lease, Term of Contract	20 years		20 years
Renewal term	5 years		5 years
Texas
Lessee, Lease, Description [Line Items]
Number Of Restaurant Closed | restaurant		1		1
Number of restaurants primarily responsible for impairment | restaurant			1
Property lease modification [Member]
Lessee, Lease, Description [Line Items]
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 1,400	$ 1,200	$ 1,700	$ 1,200
Property Lease [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Payments			9,269	12,361
Finance Lease, Right-of-Use Asset, Amortization		3		9
Finance Lease, Interest Expense	5	7	11	15
Operating Lease, Cost	6,545	6,585	13,075	13,187
Variable Lease, Cost	105	127	209	224
Sublease Income	(763)	(511)	(1,541)	(901)
Total lease cost	$ 5,892	$ 6,211	11,754	12,534
Finance Lease, Principal Payments			16	53
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			1,650	$ 4,995
Derecognition of ROU assets due to terminations, impairment or modifications			$ (543)
Finance Lease, Weighted Average Remaining Lease Term	2 years 3 months 29 days	3 years 3 months 29 days	2 years 3 months 29 days	3 years 3 months 29 days
Operating Lease, Weighted Average Discount Rate, Percent	4.34%	4.38%	4.34%	4.38%
Operating Lease, Weighted Average Remaining Lease Term	11 years 8 months 23 days	12 years 2 months 23 days	11 years 8 months 23 days	12 years 2 months 23 days
Finance Lease, Weighted Average Discount Rate, Percent	11.10%	11.10%	11.10%	11.10%
Equipment Lease [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Payments			$ 619	$ 654
Operating Lease, Cost	$ 307	$ 327	614	654
Short-term Lease, Cost	5	9	12	17
Variable Lease, Cost	45	27	70	98
Total lease cost	$ 357	$ 363	696	$ 769
Finance Lease, Principal Payments			0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability			12
Derecognition of ROU assets due to terminations, impairment or modifications			$ (15)
Finance Lease, Weighted Average Remaining Lease Term	0 years	0 years	0 years	0 years
Operating Lease, Weighted Average Discount Rate, Percent	3.93%	3.98%	3.93%	3.98%
Operating Lease, Weighted Average Remaining Lease Term	2 years 8 months 26 days	3 years 6 months 18 days	2 years 8 months 26 days	3 years 6 months 18 days
Finance Lease, Weighted Average Discount Rate, Percent	0.00%		0.00%
Lease Not Yet Commenced [Member]
Lessee, Lease, Description [Line Items]
Number Of Leases | lease			0